Simon Leigh is an addiction counsellor accredited by the Federation of Drug and Alcohol Professionals who also gives talks in schools on drugs (www.addictiontherapy.org.uk)

Sometimes it's scary just how much children know at such a young age. I talk to them like adults. It's one of the reasons schools invite me in. Unlike parents or teachers I don't say: 'You mustn't do this'. I just give them the facts, but in a way that leaves them wondering why anyone would want to take drugs.

The questions I'm asked can be very telling. My talks are very interactive and I can usually clock who has addiction in the family or an alcoholic parent just by the questions the kids ask.

I also talk to the parents separately after school. I will give them the same talk that I gave their kids so they know what they're learning. Most parents haven't got a clue about drugs. Many will have tried drugs 20 or 30 years ago and some may be doing it today - coke or the odd joint - but for most of the parents I talk to the drugs today are very different to the drugs they knew years ago.

A lot of parents are in absolute denial about addiction happening to their children, but it is a mental illness and it doesn't discriminate between age, sex, race or religion. It will affect anybody.

When you tell the parents that people can be genetically predisposed to addiction some of them go white. You can tell who might have it in the family.

Many people want me to teach them how to be parents. I won't do it. They'll ask, 'Do I let them smoke dope at home?' That's a decision they have to make for themselves. Personally I wouldn't condone the use of drugs by my kids in my house, but I can't tell parents how to deal with their kids.

During my work as a counsellor, I have been amazed by what some of the kids are up to. I once saw a 14-year-old boy who had been injecting heroin since he was 10 and another girl who was turning tricks with her mother from the age of 12 in order to fund her mother's habit. There's some sick stuff going on.

Many parents ask: how would I know if my child is doing drugs? I tell them what to look for - lethargy, erratic behaviour, insomnia - but when it comes to cannabis, I tell them not to panic. There is a correlation between smoking cannabis and mental-health problems, but the percentage is small.

I'm also looking to educate the kids so that if someone hands them a brown powder and says, 'Here's some cannabis - try this,' they'll know it might actually be heroin, because if you've never done it before you won't know. However, I never glamorise the use of drugs.

One reason for talking to kids is to try to rid this country of the stigma surrounding addiction. It's an illness affecting around 10 per cent of the population and so should not have any shame attached to it.

The fact that the kids are looking at a real-life addict gives me a lot of credibility. I've been in recovery for cocaine addiction for several years so I use my own experiences when I give talks.